Foods, their selection and preparation

Yeasts for Leavening. Yeasts are microscopic one-celled plants which multiply by budding. When alive and active these tiny organisms are able to ferment or break down sugar with the liberation of carbon dioxide. The steps in the fermentation are indicated as follows: Starch + diastase (enzyme in flour) + water = dextrins + maltose Maltose + maltase (enzyme in flour) = glucose Glucose + zymase (enzyme from yeast) = alcohol and carbon dioxide [292] Approximate Comparative Kind Acid Component Rate2 Amount for Oven 1 Cup Flour Temperature3 Teaspoons Table LXI Tartrate 1. Cream of tartar orr 1^ to 2 Higher Comparison of 2. Cream of tartar + tartaric acid Higher Different Kinds Phosphate 1. Monocalcium phosphate, 1^ to 2 Higher of Baking Powder1 hydrate or 2. Monocalcium phosphate, 1 to Lower anhydrous Sodium aluminum Monocalcium phosphate + 1 to 1^ Lower sulphate or combisodium aluminum sulnation . phate The carbon dioxide so liberated is retained by the gluten of the bread, or other batter or dough. The leavening is in proportion to the amount of gas so formed and re¬ tained. The alcohol is driven off during bak¬ ing and probably contributes somewhat to the leavening. Leavening bread by fermentative changes is the oldest method known and is still the method in most general use throughout the world. This was at first a more or less hap¬ hazard method and was controlled only in¬ directly by changing the conditions under which the bread was mixed and raised. With the development of the science of microbi¬ ology and the study of the microorganisms in relation to their application in breadmaking, the fermentation of bread has been worked out as a very definite and exact science. The most desirable yeasts have been isolated and studied in detail. They are now avail¬ able in fairly pure cultures. Furthermore, the process of making yeast-leavened breads can be controlled and the conditions provided under which the yeast will develop best. xBy reading the label on the can one can identify the kind of powder. 2The figures 1 to 5 indicate the rate of reaction. One is the most rapid and 5 is the slowest. 3A slightly lower oven temperature may be used for those powders which work most slowly. (See page 303.) Yeast is available to the consumer as moist or compressed yeast and as dry yeast. Com¬ pressed yeast comes in cakes and dry yeast in granular form in envelopes or packages. Compressed Yeast. Compressed yeast contains active living yeast cells. It is put up in the form of cakes composed of millions of these cells. In the preparation of the cakes, the well-washed yeast is mixed with a small amount of starch, pressed, and cut into cakes of the desired size. The cakes are wrapped in tinfoil and kept under refrigeration until dis¬ tributed for use. The amount of starch that is added varies somewhat. Its use is justified on the ground that a better cake is formed than from the yeast cells alone, and that the starch acts as a drier, making the yeast keep better. Twenty per cent is usually consid¬ ered the limit of the amount of starch used in compressed yeast.